Via fill compositions for direct attach of devices and methods for applying same

ABSTRACT

The present invention permits solder joints to be made directly to via and through holes without the solder being wicked into the vias or through holes, by filling plated through holes with an epoxy or cyanate fill composition. When cured and overplated, the fill composition provides support for the solder joint and provides a flat solderable surface for the inter-connection. In certain embodiments, the cured fill compositions, offer a further advantage of being conductive. The invention also relates to several novel methods for filling through holes with such fill compositions, and to resistors located in through holes and vias.

BACKGROUND OF THE INVENTION

In circuit board construction, solder ball connection of a module, suchas a ceramic module, provides significant electrical performanceadvantage over conventional pin-in-hole technology. Pin-in-holetechnology involves the attachment of modules to circuit boards usingprojections or pins which insert into corresponding holes in the board.

Pin-in-hole connections, due to mechanical considerations, occupyconsiderable surface area of the circuit board thwarting furtherminiaturization. In contrast, solder ball technology attaches modules tothe board using balls of solder on the module which are joined tocorresponding contact points on the surface of the board.

Specifically, a high melting point solder ball is placed on the backsideof a module and attached to the module with a low melting point solderpaste reflow process. The module is then attached to the surface of thecircuit board with a screened, low melting point solder paste. Sinceattachment of the module to the board is made only on the surface of theboard, the attachment land, drill diameter, and clearance land sizes maybe reduced in size, thus allowing greater wiring area. Solder ballconnection provides the advantage of enhanced system speed because thesignal net length is reduced and also provides the advantage of enhancedwiring capability due to reduced via and land diameters.

However, a problem with solder ball connect technology occurs where thesolder ball connection is being made to a conventional through hole orvia. When such a connection has been attempted, the screened eutecticpaste used to connect the solder ball to the board flows through thehole away from the intended inter-connection site during the reflowingprocess. This results in poor and unreliable solder joints. One attemptto attach a module directly to a via in pad type of land was to pre-fillthe through holes with solder to create a solid land prior to attachmentof the solder ball. However, the solder is pulled down through the hole,away from the interconnection during the assembly of the circuit board.This pulling down or "wicking" of the solder results in a void below theball which leads to cracking and thus produces poor, unreliable solderjoints.

Another solution to the problem of connecting solder balls to throughholes has been to utilize a "dog-bone" type termination where a solidcopper land is displaced from the plated through hole or via. The solderjoint is made to the solid copper land which is then connected by acircuit line to the via or through hole. While the dog bone terminationprovides excellent solder joints, it decreases the advantages otherwiseobtained with the via in pad solder ball connection technology becausethe wireability is reduced and the signal line length is increased.Concomitantly, the circuit line occupies space or "real estate" on thesurface of the circuit board.

Attempts have also been made to fill vias and through holes with certainpolymer materials, but such polymer materials incompletely fill the viasthereby creating significant voids. Such polymer materials also requirelengthy processing time due to drying of the solvent. These polymermaterials also tend to shrink as the solvent is released, thus causingnon-planar surfaces and additional voids. A still further drawback withsuch materials is limited solderability.

It would be desirable to have solder ball connections directly atthrough holes thereby consuming less real estate, decreasing signal linelength and increasing wireability, and yet exhibiting satisfactorysolder joints.

SUMMARY OF THE INVENTION

The present invention permits solder joints to be made directly to viasand through holes without the solder being wicked into the vias orthrough holes, by filling plated through holes with an epoxy or cyanatefill composition. When cured and overplated, the fill compositionprovides support for the solder ball and provides a flat solderablesurface for the inter-connection. The cured fill compositions offer afurther advantage of being electrically conductive. The invention alsorelates to several novel methods for filling apertures such as throughholes with such fill compositions, and to resistors located in suchapertures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional, not to scale view showing a plated throughhole, filled with the epoxy composition of the present invention whichends of the filled through hole are covered with a layer of copper.Disposed on the copper layer is a solder ball.

FIG. 2 is a diagrammatic representation of the positive displacementpump system used in the injection method.

FIG. 3 is a cross sectional, not to scale view showing the sacrificialcarrier coated with fill composition and applied to a substrate.

FIG. 4 is a cross sectional, not to scale view showing a substrate withapertures filled by the sacrificial carrier method.

DETAILED DESCRIPTION OF THE INVENTION

The present invention permits solder joints to be made directly to viasand to through holes without the solder being wicked into the throughholes, by filling both plated or unplated through holes and vias with anepoxy or cyanate fill composition. When cured and overplated, the fillcomposition provides support for the solder ball and provides a flatsolderable surface for the inter-connection eliminating the path for thesolder to pull away from the solder joint. The presence of electricallyconductive powder such as copper in the fill composition offers afurther advantage of being electrically conductive, thermally stable andsolderable. The invention also relates to several novel methods forfilling through holes and vias in substrates, such as circuit carrierswith such fill compositions. Circuit carriers include, for example,circuit boards, cards, ceramic substrates, organic or inorganicmulti-chip modules, organic or inorganic single chip modules.

Shown in FIG. 1, is a substrate 12, having a through hole 14 filled withfill composition 16. Disposed atop of the filled through hole 14 is pad18 atop of which is low melting point solder 20. On top of solder 20 issolder ball 22 which has disposed on top solder 24. Chip carrier 26,which is shown with a chip attached, is disposed atop of solder 24.

The preferred printed circuit board includes conventional FR-4 Epoxy andlaminates based on high temperature resins such as high temperatureepoxies, polyimides, cyanates (triazines), fluoropolymers, ceramicfilled fluoropolymers, benzocyclobutenes, perfluorobutanes,polyphenylenesulfide, polysulfones, polyetherimides, polyetherketones,polyphenylquinoxalines, polybenzoxazoles, and polyphenylbenzobisthiazoles, combinations thereof and the like.

THE FILL COMPOSITION

The fill composition contains an electrically conductive powder, acatalyst and a binder; specifically the binder composition is either anepoxy composition or a cyanate composition. The epoxy composition iscomprised of epoxy resin, curing agent, conductive powder and catalyst.The epoxy resin is either a cycloaliphatic epoxy resin or an epoxycresol novolac resin. Depending on the epoxy resin used additionalcomponents are also employed. The fill compositions may be used to fillapertures including, for example, vias, through holes, including platedthrough holes and non-plated through holes. Depending on the desired useof the aperture, the fill composition can be electrically conductive orelectrically insulating. Certain fill compositions are used to formresistors having a controlled selected electrical resistance withinapertures.

The Conductive Powder

The conductive powder contains electrically conductive powder, includingcarbon powders and metal powders, such as copper, silver, nickel,molybdenum, gold, palladium, platinum, aluminum powder and mixturesthereof, having an average particle size of 0.1 to 75 microns,preferably 0.5 microns to 25 microns, more preferably about 0.5 to about10 microns. Suitable copper powders are commercially available fromAlcan Powders & Pigments or Metz Metallurgical Corporation. Optionally,electrically insulating powders such as aluminum oxide, 92% alumina, 96%alumina, aluminum nitride, silicon nitride, silicon carbide, berylliumoxide, boron nitride and diamond powder either high pressure or PlasmaCVD may be added to the conductive powder. The thermal conductivity ofthe thermally conductive powder is preferably from about 0.8 to about1.4 W/m.K.

The amount of electrically conductive powder is added either to providea fill composition having controlled resistivity to form a resistor, orto provide a fill composition that forms an electrical conductor.

The epoxy compositions of the present invention contain about 5 to about65% preferably about 8 to about 40% of the combined binder andconductive powder weight, of the binder, and correspondingly about 35 toabout 95%, preferably about 60% to about 92% of the combined binder andconductive powder weight, of the thermally conductive powder. As usedherein "binder" means the nonmetal and nonsolvent components of the fillcomposition.

THE EPOXY FILL COMPOSITION

The Cycloaliphatic Epoxy Fill Composition Embodiment

The cycloaliphatic epoxy composition comprises: about 35 to about 95%,preferably about 60 to about 92% conductive powder based on combinedbinder and conductive powder weight; and about 5 to about 65%,preferably about 8 to about 40% binder, based on combined binder andconductive powder weight. The binder comprises: about 25 to about 75%,preferably about 30 to about 60% by weight cycloaliphatic epoxy resin;about 25 to about 75%, preferably about 30 to about 40%, by weight ofanhydride curing agent; catalyst, in an amount sufficient to catalyzethe curing of the cycloaliphatic epoxy resin, preferably about 0.05% toabout 10%, more preferably about 1% to about 5%, by weight; andoptionally, about 0% to about 25%, preferably about 5% to about 20% ofthe binder weight, of a flexibilizer.

Since the cycloaliphatic epoxy composition does not require a solvent,significant time is saved in processing by not having to dry thecycloaliphatic epoxy composition. The cycloaliphatic epoxy compositionsof the present invention are free, or substantially free, that is lessthan 0.2% by weight, of non-reactive organic solvents.

The preferred cycloaliphatic epoxy resins are non-glycidyl etherepoxides containing more than one 1,2 epoxy group per molecule. Theseare generally prepared by epoxidizing unsaturated aromatic hydrocarboncompounds, such as cyclo-olefins, using hydrogen peroxide or peracidssuch as peracetic acid and perbenzoic acid. The organic peracids aregenerally prepared by reacting hydrogen peroxide with either carboxylicacids, acid chlorides, or ketones to give the compound R--COOOH. Thesematerials are well known, and their synthesis and description may befound in Byrdson, J., Plastic Materials, (1966), p. 471. Suchnon-glycidyl ether cycloaliphatic epoxy resins have a ring structurewherein the epoxide group is part of the ring or is attached to the ringstructure. These epoxy resins may also contain ester linkages. Suitablenonglycidyl ether cycloaliphatic epoxy resins have the followingstructures: ##STR1## wherein: S is a saturated ring structure,

R' selected from the group of CHOCH₂, O(CH₂)_(n) CHOCH₂ and OC(CH₃)₂CHOCH₂ radicals;

R" is selected from the group of CH₂ OOC, and CH₂ OOC(CH₂)₄ COOradicals.

Examples of suitable non-glycidyl ether cycloaliphatic epoxides include3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate;vinylcyclohexane dioxide which contains two epoxide groups, one of whichis part of a ring structure;3,4-epoxy-6-methylcyclohexylmethyl-3,4-epoxycyclohexane carboxylate anddicyclopentadiene dioxide.

Other cycloaliphatic epoxy resins are suitable, including glycidylethers such as: 1,2-bis(2,3-epoxycyclopentyloxy)-ethane;2,3-epoxycyclopentyl glycidyl ether; diglycidylcyclohexane-1,2-dicarboxylate; 3,4-epoxycyclohexyl glycidyl ether;bis-(2,3-epoxycyclopentyl) ether; bis-(3,4-epoxycyclohexyl) ether;5(6)-glycidyl-2(1,2-epoxyethyl)bicyclo 2.2.1!heptane;cyclohexa-1,3-diene dioxide or 3,4-epoxy-6-methylcyclohexylmethyl3",4"-epoxy-6'-methylcyclohexanecarboxylate.

Also suitable are epoxy resins in which the 1,2-epoxy groups areattached to various heteroatoms or functional groups; such compoundsinclude, for example, the N,N,O-triglycidyl derivative of 4-aminophenol,the N,N,O-triglycidyl derivative of 3-aminophenol, the glycidylether/glycidyl ester of salicylic acid,N-glycicyl-N'-(2-glycidyloxypropyl)-5,5-dimethylhydantoin or2-glycidyloxy-1,3-bis-(5,5-dimethyl-1-glycidylhydantoin-3-yl)propane.Mixtures of cycloaliphatic epoxy resins are also suitable.

The preferred cycloaliphatic epoxy resins include3,4-epoxycyclohexylmethyl-3-4-epoxycyclohexanecarboxylate, (systematicname: 7-oxabicyclo(4.10)heptane-3-carboxylic acid7-oxabicyclo(4.1)hept-3-ylmethyl ester) commercially available under thedesignation ERL-4221 from Union Carbide Company and3,4-epoxycyclohexylmethyl-3-4-epoxycyclohexane carboxylate mixed withbis(3,4-epoxycyclohexyl) adipate, available under the designationERL-4299 from Union Carbide Company.

The cycloaliphatic epoxy resins have a preferred epoxy equivalent weightfrom about 50 to about 500, preferably from about 50 to about 250. Thecycloaliphatic epoxy resins have a viscosity less than about 1000 cps at25° C., preferably about 5 to about 900 cps, more preferably about 300to about 600 centipoise and most preferably about 300 to about 450centipoise. The cycloaliphatic epoxy resins have a molecular weight offrom about 200 to about 800, more preferably from about 200 to about700, most preferably about 200 to about 500 and a weight per epoxide ofabout 50 to about 500, preferably about 50 to about 300. The glasstransition temperature of the fill composition is above 130° C.,preferably above 140° C. Accordingly, epoxy resins including thecycloaliphatic epoxy resin and mixtures thereof, are selected so as toprovide the epoxy composition with a glass transition temperature above130° C.

The Curing Agent

The curing agents used to cure the cycloaliphatic epoxy resin areanhydrides derived from a carboxylic acid which possesses at least oneanhydride group. The carboxylic acids used in the formation of theanhydrides may be saturated, unsaturated, aliphatic, cycloaliphatic,aromatic or heterocyclic. Examples of these anhydrides include, amongothers, phthalic anhydride, isophtalic anhydride, dihydrophthalicanhydride, tetrahydrophthalic anhydride and hexahydrophthalic anhydride,1,3,5,6,7,7-hexachloro-3,6-endomethylene 1,2,3,6 tetrahydrophthalicanhydride (chlorendic anhydride), succinic anhydride, maleic anhydride,chlorosuccinic anhydride, monochloromaleic anhydride,6-ethyl-4-cyclohexadiene, 1,2-dicarboxylic acid anhydride,3,6-dimethyl-4-cyclohexadiene-1,2-dicarboxylic acid anhydride,6-butyl-3,5-cyclohexanediene-1,2-dicarboxylic acid anhydride,octadecylsuccinic acid anhydride, dodecylsuccinic acid anhydride,dioctyl succinic anhydride, nonadecadienylsuccinic anhydride,3-methoxy-1,2,3,6-tetrahydrophthalic acid anhydride,3-butoxy-1,2,3,6-tetrahydrophthalic anhydride, pyromellitic anhydride,di, tetra, and hexahydropyromellitic anhydride, polyadipic acidanhydride, polysebasic anhydride, and the like and mixtures thereof.Preferred anhydrides include: aromatic monoanhydrides; aromaticdianhydrides, such as pyromellitic anhydride; aliphatic monoanhydrides;cycloaliphatic monoanhydrides; and the chlorinated derivatives thereof.Especially preferred are the normally liquid or low melting anhydrides.

Other suitable curing agents include the trimellitic anhydride,benzophenone tetracarboxylic dianhydrides, polyfunctional cyclicanhydrides including pyromellitic tetracarboxylic acid dianhydride,cyclopentane tetracarboxylic acid dianhydride, diphenylethertetracarboxylic acid dianhydride, the hexacarboxylic acid trianhydrideof benzene, cyclohexane. Other suitable curing agents include linear orcyclic anhydrides of any of the following acids: oxalic acid, malonic,glutaric, adipic, pimelic, azelaic, sebacic, brassidic, trimellitic,dimer fatty acid and the polyester acid, such as the diacid from anexcess of azelaic acid, and neopentyl glycol sold under the tradename"Emery Diacid", by Emery Chemical Company and having an equivalentweight of 500.

The anhydride curing agent is generally employed in amounts constitutingon an equivalent basis, about 20% to about 120%, preferably about 80 to110% of the cycloaliphatic epoxy resin and preferably about 75% to about100% of the epoxide equivalents.

The Catalyst

A catalyst is added in an effective amount to promote the crosslinkingof the epoxy resin. Suitable catalysts for the epoxy resins include, forexample, amines such as the tertiary amines and acidic catalysts such asstannous octoate, and imidazoles. Suitable tertiary amine catalystsinclude N,N-dimethylbenzylamine, triethylamine, N,N-dimethylaniline,N-methylmorpholine, N-ethylmorpholine, imidazole and tetrachloromethylethylene amine, tetramethyl guanidine, triisopropylamine, pyridine,piperrazine, triethyamine, tributylamine, dimethyl benzylamine,triphenyl amine, tricyclohexylamine, quinoline, triethylamines,triphenylamine, tri(2,3-dimethyl cyclohexyl)amine, benzyldimethylamine,1,3-tetramethyl butane diamine, tris (dimethylaminomethyl) phenol, andtriethylenediamine. Suitable imidazoles have one or more alkyl of 1 to 6carbon atoms or aryl which can be positioned on the amino nitrogen orheterocyclic carbons.

Suitable imidazoles include, for example imidazole, 2-methylimidazole,2-ethylimidazole, 2-propylimidazole, 2-butylimidazole,2-pentylimidazole, 2-hexylimidazole, 2-cyclohexylimidazole,2-phenylimidazole, 2-nonylimidazole, 2-undecylimidazole,2-heptadecylimidazole, 2-ethyl-4-methylimidazole,2-phenyl-4-methylimidazole, 1-benzylimidazole,1-ethyl-2-methylbenzimidazole, 2-methyl 5,6-benzimidazole, 1vinylimidazole, 1-allyl-2-methylimidazole, 2-cyanoimidazole,2-cyanoimidazole, 2-chloroimidazole, 2-bromoimidazole, and combinationsthereof. Other imidazoles containing oxygen, sulfur or halogen or thelike substituents include for example,1-(2-hydroxypropyl)-2-methylimidazole, 2-phenyl-4,5-dimethylolimidazole,2-phenyl-4-methyl-5-hydroxymethylimidazole, 2-chloromethylbenzimidazole,2-hydroxybenzimidazole, and any combination thereof. Most particularlysuitable are 2-methylimidazole, 2-ethyl-methylimidazole,1,2-dimethylimidazole and 2-phenylimidazole,2-phenyl-4,5-dihydroxymethylimidazole, 2-phenyl-4-methylimidazole,1-cyanaoethyl-2-methylimidazole, 1-cyanoethyl-2-phenylimidazole,3,4-dialkyl imidazoles are preferred since they provide accelerated andadvanced cure of the epoxy reaction at moderate temperature and providecured materials with the highest heat distortion temperatures.

Other suitable catalysts are the fully substituted compounds including:quaternary ammonium hydroxides and halides; quaternary phosphoniumhalides; arsines, amine oxides; aminophenols; phosphine oxides;phosphines; phosphonium halides; amines; phosphoramides;phosphineamines; and tertiary aminophenols. Mixtures of catalyst arealso suitable.

The Novolac Epoxy Fill Composition Embodiment

The novolac epoxy fill composition comprises: about 60% to about 95%,preferably about 70% to about 92% conductive powder based on combinedbinder and conductive powder weight; about 5 to about 40%, preferablyabout 8 to about 30% binder, based on combined binder and conductivepowder weight; and solvent. The solvent is present from about 10% toabout 60%, preferably about 20% to about 50%, more preferably about 20%to 30% of the combined binder, conductive powder and solvent weight. Thebinder comprises: about 20% to about 60%, preferably about 25% to about60% novolac epoxy resin; about 20% to about 60%, preferably about 25% toabout 60% curing agent; catalyst, in an amount sufficient to catalyzethe curing of the novolac epoxy resin, preferably about 0.05% to about10%, more preferably about 0.5% to about 3%, by weight; and optionally,0% to about 30%, preferably about 5% to about 20% of the binder weight,of a flexiblizer. These amounts are based upon the total amounts ofbinder and conductive powder in the composition. The novolac epoxyresins have weight per epoxide of about 200 to about 500.

Suitable novolac epoxy resins are commercially available and includenovolac epoxy resins obtained by reacting, preferably in the presence ofbasic catalyst such as sodium hydroxide, an epihalohydrin such asepichlorohydrin with a novolac resin. Novolac resins are the resinouscondensate of an aldehyde such as formaldehyde, and either a monohydricphenol, dihydric or a polyhydric phenol. The dihydric phenols includephenols substituted with one or more groups selected from: hydrogen,bromine and chlorine and wherein the aromatic rings are joined by: analkylene (e.g. methylene) or alkylidene (e.g. isopropylidene) grouphaving from about 1 to about 4 carbon atoms, S, S--S, SO, SO₂, CO, or O.

Suitable novolacs are derived from the following phenols: phenol,cresol, alpha and beta-naphthol, o-, m-, or p-chlorophenol, alkylatedderivatives of phenol, including for example, o-methyl-phenol,3,5-dimethylphenol, p-t-butyl-phenol and p-nonylphenol and othermonohydric phenols, as well as polyhydric phenols, such as resorcinoland hydroquinone. The polyhydric phenols having from 2 to 6 hydroxylgroups and having from 6 to about 30 carbon atoms are particularlyuseful in the reaction with epoxy resins to form either linear orcrosslinked high molecular weight resins. Novolacs derived frompolyhydric phenols include for example, phenol which contain substitutedgroups including halogen (fluoro, chloro or bromo or hydrocarbyl and thearomatic rings are joined by a group selected from: oxygen, sulfur, SO,SO₂, bivalent hydrocarbon radicals containing up to 10 carbon atoms, andoxygen, sulfur and nitrogen containing hydrocarbon radicals, such as:OR'O, OR'OR'O, SR'S, SR'SR'S, OSiO, OSiOSiO, OCOR'COO, COOR'COO, SOR'SOand S0₂ R'SO₂ radicals wherein R' is a bivalent hydrocarbon radical.

An illustrative, but by no means exhaustive listing of suitable dihydricphenols includes 4,4'-dihydroxydiphenylmethylmethane, (Bis-phenol A),2,4'-dihydroxydiphenylmethylmethane,3,3'-dihydroxydiphenyldiethylmethane,3,4'-dihydroxydiphenylmethylpropylmethane,2,3'-dihydroxydiphenylethylphenylmethane,4,4'-dihydroxydiphenylpropylphenylmethane,4,4'-dihydroxydiphenylbutylphenylmethane,2,2'-dihydroxydiphenylditolylmethane,4,4'-dihydroxydiphenyltolylmethylmethane, and the like.4,4'-isopropylidenediphenol (bisphenol A) is the preferred phenol.Suitable epoxidized novolac resins include, for example, the diglycidylethers of resorcinol, catechol, hydroquinone, bisphenol, bisphenol A,bisphenol K, tetrabromobisphenol A, phenol-aldehyde novolac resins,alkyl substituted phenol-aldehyde novolac resins, alkyl substitutedphenol-formaldehyde resins, phenol-hydroxybenzaldehyde resins,cresol-hydroxybenzaldehyde resins, dicyclopentadiene-phenol resins,dicyclopentadiene-substituted phenol resins, bisphenol F,tetramethylbiphenol, tetramethyltetrabrobiphenol,tetramethyltribromobiphenol, tetrachlorobisphenol A, and combinationsthereof.

Also suitable epoxidized novolac resins include the glycidyl ethers ofcompounds having an average of more than one aliphatic hydroxyl permolecule such as for example, aliphatic diols, polyether diols,polyether tetraols, and combinations thereof. Also suitable are thealkylene oxide adducts of compounds containing an average of more thanone aromatic hydroxyl group per molecule such as, for example, theethylene oxide, propylene oxide, or butylene oxide adducts of dihydroxyphenols, biphenols, bisphenols, halogenated bisphenols, alkylatedbisphenols, trisphenols, phenol-aldehyde novolac resins, halogenatedphenol-aldehyde novolac resins, alkylated phenol-aldehyde novolacresins, hydrocarbon-phenol resins, hydrocarbon-halogenated phenolresins, or hydrocarbon-alkylated resins, or any combination thereof.

A suitable novolac epoxy resin is available under the trade designation8212 from Ciba-Geigy. The 8212 resin is a tetrabromo bisphenol A curednovolac resin catalyzed with methyl imidazole. The 8212 resin alsocontains the solvent methyl ethyl ketone. The bromine content is about29%. The precise chemical composition of the 8212 is proprietary. The8212 resin has a weight per epoxide of about 230 to about 400, 70%solids, and a final glass transition temperature of about 165° C. toabout 175° C. Other novolac epoxy resins have such or similar propertieswould also be suitable. The 8212 resin contains an epoxy cresol novolakresin designated "ECN 1280" commercially available from Ciba Geigy. TheECN 1280 resin which has an epoxide equivalent weight of about 235, anda melting point of about 80° C., sold by Ciba Geigy, is also suitable.Another suitable resin, having similar properties to the ECN 1280 resin,is available under the trade designation "ECN 1299" from Ciba Geigy.

Curing agents

Suitable curing agents for the epoxy novolac resin include conventionalphenol-novolac curing agents for a phenol-novolac resin, cresol-novolacresin, and alkyl modified phenol resin, a bisphenol A-novolac resin anda multifunctional phenol resin such as tris(hydroxyphenyl)methane.However, the curing agent should not be restricted to these curingagents. The usage is not restricted to the use of a single curing agent,and two or more curing agents can be used in combination. The preferredcuring agent is tetrabromo Bisphenol A.

Suitable curing agents aromatic hydroxyl containing compounds which canbe employed herein include, for example compounds having an average ofmore than one phenolic hydroxyl group per molecule. Suitable suchcompounds include, for example, dihydroxy phenols, biphenols,bisphenols, halogenated bisphenols, alkylated bisphenols, trisphenols,phenol-aldehyde novolac resins, alkylated phenol-aldehyde novolacresins, phenol-hydroxy benzaldehyde resins, alkylatedphenol-hydroxybenzaldehyde resins, hydrocarbon-phenol resins,hydrocarbon-halogenated phenol resins, hydrocarbon alkylated phenolresins, and any combination thereof. Particularly suitable aromatichydroxyl containing compounds include for example those represented bythe formulae: ##STR2## wherein: each A' is independently a divalenthydrocarbyl group having from 1 to about 9, preferably from 1 to about 4carbon atoms or --O--, --SO₂ --, or --CO--;

Q is a hydrocarbyl group having from 1 to about 10 carbon atoms;

Q' is hydrogen or an alkyl group having from 1 to about 4 carbon atoms;

Y is independently hydrogen, bromine, chlorine, or a hydrocarbyl grouphaving from 1 to about 9, preferably from 1 to about 4 carbon atoms; mhas a value from about 0.01 to about 10, preferably from about 0.1 toabout 8, more preferably from about 0.5 to about 6.

The term hydrocarbyl means any aliphatic, cycloaliphatic, aromatic, oraryl substituted aliphatic or cycloaliphatic groups or aliphatic orcycloaliphatic substituted aromatic groups. The aliphatic groups can besaturated or unsaturated. Likewise the term hydrocarbyloxy means ahydrocarbyl group having an oxygen linkage between it and the carbonatom to which it is attached. The preferred curing agent is tetrabromobisphenol A.

The solvent

In the epoxy novolak composition, a solvent is employed to providesuitable viscosity for screening and coating. Suitable solvents include,for example, ketones, such as acetone or methyl ethyl ketone. Methylethyl ketone is preferred.

Other epoxy resins

Other epoxy resins may be added to the fill composition. Suitable resinsinclude, the diglycidyl ethers of resorcinol, catechol, hydroquinone,biphenol, bisphenol A, bisphenol K, tetrabromobisphenol A. Suitableresins include a diglycidyl ether of Bisphenol A, having an epoxyequivalent weight of about 185 to about 195 with a viscosity of about12000 cps., commercially available as Epon 828 from Shell Chemical.

Optional Ingredients to the Epoxy Fill Compositions

The Flexibilizer

Optionally although preferably, a reactive modifier, also known as a"flexibilizer" is added to the cycloaliphatic epoxy composition toimpart flexibility and thermal shock resistance to the curedcycloaliphatic epoxy composition. Examples of suitable flexibilizersinclude: fatty acids; fatty acid anhydrides such as polyazelaicpolyanhydride and dodecenylsuccinic anhydride; diols such as ethyleneglycol, polyols, polyetherdiols such as polymers of ethylene glycolpolyethylene glycol and polypropylene glycol, and other materials havinghydroxyl groups, carboxyl epoxy, and/or carboxylic anhydridefunctionality. Other suitable flexibilizers include trihydric anddihydric carboxyl-terminated, carboxylic anhydride-terminated,glycidyl-terminated and hydroxyl-terminated polypropylene glycols orpolybutylene glycols.

Optionally, flexibilizers are also added to impart flexibility and crackresistance to the epoxy novolak fill composition. Suitable flexibilizersinclude modified hydroxy terminated silicones having the generalformulae: ##STR3## where n is an integer from 10 to 300. ##STR4##

Elastomeric carboxyl-terminated hydroxyl-terminated, mercapto-terminatedor glycidyl ether-terminated copolymers based on butadiene, and polar,ethylenically unsaturated comonomers are also suitable flexibilizers.The number average molecular weight of the flexibilizer is between 500and 6,000, preferably between 1,000 and 2,500. Suitable flexibilizersinclude polycaprolactone polyol based prepolymer having an averagemolecular weight of about 1200, commercially available as Tone 0231 fromUnion Carbide, and an epoxidized butadiene prepolymer, having an averagemolecular weight of about 1200 to 1300, commercially available as PolyBd 605 from Elf Atochem North America Inc.

Surfactants

Optionally, surface active agents, referred to herein as "surfactants",are added to the epoxy composition to facilitate mixing the thermallyconductive powder with the epoxy resin. When used, the surfactants arepresent in amounts of about 0.5% to about 3% and preferably about 1.2%to about 1.6% of the combined weight of the binder and the thermallyconductive powder. Suitable surfactants include non-ionic type surfaceactive agents, such as Triton X-100 from Rohm and Haas Co. Suitablenon-ionic surface active agents include for example, surfactantsprepared by the reaction of octylphenol or nonylphenol with ethyleneoxide.

The epoxy composition may optionally contain other curing promoters oraccelerators and various other materials such as plasticizers,elastomers, fillers, pigments, and surface treating agents.

Optionally, surface treating agents added to the epoxy compositioninclude for example, vinyltrimethoxysilane, vinyltriethoxysilane,N(2-aminoethyl) 3-aminopropylmethyldimethoxysilane,3-aminopropylethoxysilane, 3-glycidoxypropyl trimethoxysilane,3-glycidoxypropylmethyl dimethoxysilane, and mixtures thereof. Theamount of the surface treating agent used is preferably from 1 to 10parts, more preferably from 1 to 5 parts, with respect to 100 parts ofepoxy resin. Surf ace treating agent is used to provide moistureresistance and improved adhesion.

Cyanate Fill Composition

The cyanate fill composition comprises: from about 5% to about 65%,preferably about 8% to about 40% of a binder; and about 35% to about95%, preferably about 60 to about 92% of the total fill compositionweight of conductive powder. The binder comprises: catalyst in an amountsufficient to catalyze the curing of the resin, preferably about 0.05%to about 5%, more preferably about 0.1% to about 2% of the total binderweight; and resin from about 95% to about 99.95%, more preferably about98% to about 99.9% of the total binder weight. The resin in the cyanateester fill composition comprises cyanate ester resin and optionally maycontain other epoxy resins including, for example, cycloaliphatic epoxyresin, novolak resin, diglycidyl ether of bisphenol A, or mixturesthereof.

The cyanate ester resins have two or more (--O--C═N groups and arecurable through cyclotrimerization. The cyanate ester resins can bemonomeric or less preferably polymeric, including oligomers. The cyanateester resins contain the following group: ##STR5## wherein A is a singlebond or selected from: C(CH₃)(H); SO₂ ; O; C(CF₂)₂ ; CH₂ OCH₂ ; S;C(═O); OC(═O); S(═O); OP(═O)O; OP(═O)(═O)O; divalent alkylene radicalssuch as CH₂ and C(CH₃)₂ ; divalent alkylene radicals interrupted byheteroatoms in the chain such as O, S, and N;

R is selected from the group of hydrogen, halogen and alkyl groupscontaining 1 to 9 carbon atoms;

n is an integer from 0 to 4.

Suitable cyanate ester include difunctional, polyfunctional andpolyaromatic cyanate esters.

Suitable polyfunctional cyanates prepared by well known methods, forexample, by reacting the corresponding polyvalent phenol with ahalogenated cyanate in the presence of a tertiary amine such as triethylamine as exemplified in U.S. Pat. Nos. 3,553,244, 3,740,348 and3,755,402.

The phenol reactant can be any aromatic compound containing one or morereactive hydroxyl groups. The phenolic reactant is preferably a di- ortri-polyhydroxy compound of the formula: ##STR6## in which each a and bis independently 0, 1, 2, or 3, and at least one a is not 0; n is withinthe range of 0 to about 8, preferably 0 to 3; each R is independentlyselected from non-interfering alkyl, aryl, alkaryl, heteroatomic,heterocyclic, carbonyloxy, carboxy, and the like ring substituents, suchas hydrogen, C₁₋₆ alkyl, C₁₋₆ allyl, C₁₋₆ alkoxy, halogen, maleimide,propargyl ether, glycidyl ether, and the like; and A is a polyvalentlinking moiety which can be, for example, aromatic, aliphatic,cycloaliphatic, polycyclic, and heteroatomic. Examples of linking moietyA include --O--, --SO₂ --, --CO--, --OCOO--, --S--, --C₁₋₁₂ --,dicyclopentadienyl, aralkyl, aryl, cycloaliphatic, and a direct bond.

Examples of other suitable cyanate ester resins include: 1,3- or1,4-dicyanatobenzene; 1,3,5-tricyanatobenzene, 1,3-, 1,4-, 1,6-, 1,8-,2,6-, or 2,7-dicyanatonaphthalene, 1,3,6-tricyanatonoaphthalene;4,4'-dicyanatobiphenyl, bis(4-cyanatophenyl) methane;2,2-bis(4-cyanatophenyl) propane,2,2-bis(3,5-dichloro-4-cyanatophenyl)-propane; bis(4-cyanatophenyl)ether; bis(4-cyanatophenyl)-thioether, bis(4-cyanatophenyl) sulfate;tris(4-cyanatophenyl) phosphite; tris(4-cyanatophenyl) phosphate;bis(3-chloro-4-cyanatophenyl) methane; cyanated novolac derived fromnovolac, cyanated bisphenol type polycarbonate oligomer derived frombisphenol type polycarbonate oligomer, and mixtures thereof.

A suitable polyaromatic cyanate ester containing cycloaliphatic bridginggroup between aromatic rings is available from Dow Chemical Companyunder the designation "Dow XU-71787 cyanate". Preferred polyfunctionalcyanate ester are: bisphenol AD dicyanate (4,4'-ethylidene bisphenoldicyanate) commercially available as AroCy-L10 from Ciba-Geigy;hexafluoro-bisphenol A dicyanate commercially available as AroCy-F40Sfrom Ciba-Geigy and bisphenol M dicyanate commercially available asRTX-366 from Ciba-Geigy. The bisphenol M dicyanate has the structure:##STR7##

Other suitable cyanate ester resins include the following commercialproducts having a dielectric constant of 2.6 to 3.1, a homopolymerhaving a glass transition temperature (Tg) of about from 250° to 290°C., available from Ciba-Geigy: REX-378, REX-379, bisphenol A dicyanatesavailable under the designations AroCy B-10, B-30, B-40S and B-50;tetramethylbisphenol F dicyanates available under the designations AroCyM-10, M-20, M-30, M-40S and M-50; and hexafluorobisphenol A dicyantes,available under the designations AroCy F-40S and F-10. As with the otherresins of the fill compositions, the preceding resins are used withvarying degrees of polymerization; for example the designation 10indicates the cyanate ester is a monomer, the designation 30 indicatesthat the cyanate resin is a semisolid resin, the designation 40Sindicates that the cyanate resin is a prepolymer solution and thedesignation 50 indicates the cyanate resin is a nonsintering solidresin.

When prepolymers of the dicyanate are employed such typically haveconversions of up to about 40% and more typically of up to about 30%. Ifno solvent is used, then, as with the cycloaliphatic resins discussedabove, preferably the cyanate ester resin should be liquid so as topermit application. Also, it is preferred that the cyanate ester resincontain no more than 40% trimerized cyanate ester resin.

Suitable catalysts for the cyanate ester resin include Lewis acids, suchas aluminum chloride, boron trifluoride, ferric chloride, titaniumchloride, and zinc chloride; salts of weak acids, such as sodiumacetate, sodium cyanide, sodium cyanate, potassium thiocyanate, sodiumbicarbonate, and sodium boronate. Preferred catalysts are metalcarboxylates and metal chelates, such as cobalt, iron, zinc, and copperacetylacetonate or octoates or naphthenates.

Solvents

Optionally solvent may be added to the cyanate fill composition.Suitable solvents include ketones, such as for example, acetone andmethyl ethyl ketone. Solvents are added from 0% to about 40%, preferablyabout 15% to about 25% of the total binder and conductive powder weight.

Method for Filling Apertures

Injection Method

The injection method uses an injection apparatus 100, and is thepreferred method of filling through holes or vias with the fillcompositions free of solvent, such as the cycloaliphatic epoxy fillcomposition and the liquid cyanate fill composition.

The injection apparatus 100 includes a positive displacement pump 102,which comprises a piston 104 within tube 106. Air cylinder 108, which isconnected to air supply 110, is connected to and powers the piston 104.Pump 102 also contains tube 111 which is connected to fill chamber 112and fill composition reservoir 114. Air supply 116 is also connected tofill composition reservoir 114. Tube 106 and tube 111 converge atchamber 112, which opens to tube 118 located within tip 120. Tip 120typically has an internal diameter of 0.008 inches and is tapered toallow sealing of the tip to the aperture. Fill composition fromreservoir 114 is forced down tube 111 into chamber 112 where piston 104forces the paste through tube 118 and out opening 130 in meteredamounts.

The injection apparatus 100 is mounted on a computer controlled X-Ytable of conventional design (not shown) which is capable of reading X-Ydata for aperture locations. Suitable dispensing equipment of the typedescribed above is available from Nova/ECD under the designation model800 or Creative Automation under the designation model 18-12. The fillcomposition is forced under pressure directly into the via without theuse of a mask. The positive displacement pump 102 forces the fillcomposition through the dispensing tip 130, which is in direct contactwith the rim of the via. The end of the tip is tapered to allow sealingof the tip to the via. This is required to displace the air in the viaduring filling. The fill compositions are applied by dispensing throughtips under pressure of about 15 psi to about 90 psi, preferably about 40psi, and temperatures of about 25° C. to about 40° C., preferably about30° C. Positioned below, and in direct contact with, substrate 122, is agas porous sheet 126, such as filter paper, which allows the air to passthrough the pores of the paper while the surface of the paper restrainsthe fill composition within aperture 132 in the substrate 122. The sheet126 is supported by a template 128 which matches the pattern, of eitherjust the aperture 132 or the substrate 122, thus allowing the airdisplaced from the aperture 132 to dissipate. The use of a positivedisplacement pump allows for precise metering of the fill composition sothat the apertures are filled to the correct level. As a result, thisminimizes the need for further mechanical processing to obtain a uniformsurface.

The fill compositions are then cured by heating from about 130° C. toabout 200° C., and preferably from about 150° C. to about 190° C., forabout 2 hours to about 4 hours, and preferably about 2 hours to about 3hours. This method of filling the apertures is suitable for a wide rangeof circuit panel thicknesses from 10-250 mils and tolerates a wide rangeof hole diameters from 4-25 mils. Since this process does not requirethe use of a mask, the costs and time associated with the mask,including building, cleaning, aligning and handling are eliminated. Fillcomposition waste is minimized because only the required amount isdispensed; indeed individual apertures can be selected for filling. Thismethod, unlike screening, insures complete filling of the apertures, andsince the vias and through holes are precisely filled, the method leavesno nubs which need to be removed.

Sacrificial Carrier Method

The sacrificial carrier method is the preferred method for fillingthrough holes and vias with fill compositions that contain solvent suchas the novolak resin compositions and cyanate compositions.

Shown in FIG. 3 is a sacrificial carrier 150 coated with fillcomposition 152 disposed on mask 154 which in turn is positioned onsubstrate 156 containing apertures 158. Sacrificial carrier 150, of aconventional material such as copper foil or polyamide, is coated with adefined thickness which is determined by the length of the aperture tobe filled, typically 1-10 mils of fill composition 152. Suitable methodsof coating the fill composition 152 onto the sacrificial carrier 150include for example screening, wire roll coating or other methods knownin the art. The composition is partially cured on the carrier 150 atfrom about 120° C. to about 140° C. preferably at about 130° C. for 3-4minutes in an oven. Mask 154 containing the drill pattern for theapertures 158 to be filled is aligned on top of the substrate 156.Preferred masks are polyamide films or copper foil. A suitable mask is afilm made from biphenyltetracarboxylic dianhydride and p-phenylenediamine, available under the designation Upilex R from UBE Industries,Japan. The coated sacrificial carrier 150 is then placed with the fillcomposition coating side down, against the mask 154, in a laminationpress (not shown). The mask 154 is predrilled with the desired patterncorresponding to the holes to be filled and aligned with substrate 156.The lamination press is then operated to force the fill compositionthrough the mask 154 into the apertures 158 at a pressure andtemperature sufficient to allow the fill composition to flow. The coatedsacrificial carrier is maintained in the lamination press at therequired pressure, e.g. from 100 psi to 350 psi, preferably about 150psi and temperature from 140° C. to about 200° C., preferably about 185°C. for 60 minutes to 190 minutes preferably 120 minutes to allow thefill composition to cure. After the lamination cycle, the sacrificialcarrier 150 and mask 154 are removed, such as by hand peeling from thesurface of the substrate 156. Any residual fill composition on thesurface of the substrate 156 is removed by conventional mechanical meanssuch as sanding, or chemical means. Vias and through holes having adiameter of 2-25 mils are filled using this method.

Shown in FIG. 4 is a substrate in which the apertures have been filledaccording to the sacrificial carrier method, after the sacrificialcarrier and mask have been removed.

Overplating

After the vias or through holes have been filled, cured and, ifnecessary, planarized by conventional methods such as sanding, they arepreferably over-plated with metal, preferably copper. Where theinjection method has been used to fill the vias or through holes,planarization is typically not needed and the filled vias and throughholes can be plated directly. Conventional seeding and plating methodssuch as acid plating or electroless plating can be used. Alternatively,where the fill composition contains metal particles the filled throughhole or via can be directly electrolessly plated. In such directplating, the metal particles in the fill composition act as a seedlayer. This method of plating eliminates the need for a seed process.The copper can be plated to any thickness desired, good results havebeen obtained with thicknesses of, about 100 to about 500 microinches;preferably about 200 to about 300 microinches. Plating durations ofabout 5 minutes to about 5 hours, preferably 10 minutes to about 60minutes are suitable. For overplating thicknesses of about 30 to about130 microinches, suitable conventional electroless baths such as ShipleyC3000, from Shipley can be used. For overplating thicknesses greaterthan about 130 microinches, suitable conventional "full build"electroless baths such as Shipley C3000, can be used, followed by anacid copper plating bath such as those available from Schering,MacDermid or Shipley.

Overplating can be performed at various stages in production of asubstrate. For example, if the through holes and vias are filled beforea subtractive circuitization step is done, a seed process, in which aconventional seed layer such as, for example palladium-tin colloid, canbe deposited on the surface of the substrate, followed by conventionalelectrolytic or electroless copper plating, and conventional subtractiveetching of circuitry.

Alternatively, where fine line subtractive circuitization is desired,the circuit lines may be etched immediately after hole fill andplanarization has been completed. Conventional subtractivecircuitization processes are used to define fine line structures in thethin, laminated copper foil. Conventional electroless copper overplatingis performed after a solder mask coating has been applied to the card.Plating will not occur in areas covered by the solder mask, and thusonly the filled hole ends and other exposed copper surfaces will beplated.

Conventional fully additive circuits may also be fabricated onsubstrates having filled holes. After hole fill and planarization, thelaminated copper foil is etched from the surface, a conventional seedlayer is applied, followed by a patterned photoresist and electrolesscopper plating of circuit lines to the desired thickness.

Alternatively, where extremely fine grid via densities are desired, forexample pad-on-pad interposer cards or direct chip attach structures,the following process sequence that only plates the filled hole ends isemployed. Following hole fill and planarization, as required, thesubstrate is etched to remove the surface metal. The substrate is thenelectrolessly copper plated without seeding. Plating occurs only on thefilled hole ends, wherein the metal particles of the hole fill materialprovide the seed or catalyst for copper deposition. Thus, plating isprecisely limited to the filled hole ends, and results in a structure ofraised copper bumps. These copper bumps may then be overplated withconventional inter-connect metals, for example nickel-gold or tin-lead,to provide pad-on-pad or direct chip attach sites. Via or inter-connectgrids of less than 0.010" can be achieved when this technique is used.

The overplating can provide a surface upon which a solder ball isplaced. As a result the solder ball is disposed over either a throughhole or via, thereby increasing the packaging density.

The filled through holes or vias of examples 1 and 2 were overplatedusing the metal in the fill composition as a seed layer for overplating.Examples 1, 2, and 5 were overplated by electroless copper plating toabout 100-300 microinches.

Resistor Embodiment

While the invention has been described primarily for conductive and ornonconductive through holes and vias, it is also possible to fill thethrough holes and vias with a fill composition having a pre-determinedelectrical resistivity to provide a resistor in a via or through hole.The resistor is a component of the circuit and has a predeterminedresistance value. Using a through hole or via to contain a resistorreduces the space on the surface of the board that is otherwise occupiedby discrete chip or pin in hole type resistors. This method alsoprovides resistors of improved tolerance, reduced cost and improvedelectrical performance over other fabricated or assembled resistors.

The fill compositions of the present invention, including the epoxy fillcompositions and the cyanate fill compositions are tailored to providethe resistor fill composition. The resistor fill composition typicallycomprises: from about 25% to about 95%, preferably about 35% to about95%, by total fill composition weight of an electrically conductivepowder; and from about 5% to about 75%, preferably from about 5% toabout 65%, by total fill composition weight, of binder.

Resistors having other resistance values may be produced by utilizingthe known resistance equation:

    R=Rho L/A

Where:

R=Resistance Value in ohms

Rho=Material Resistivity in ohm-inches

L=Resistor Length=Board Thickness

A=Cross-sectional Area

Desired resistor values may be produced by varying the board thickness,the drill diameter of the hole to be filled, the resistivity of theresistor fill composition, or combinations thereof. The resistivity ofthe resistor fill composition can be varied by modifying the percent ofthe electrically conductive powder, such as copper typically from 0-40%,or carbon typically from 0-90% in the resistor fill composition, or byadding compounds such as TaSi, NiCr, NiP, etc., or mixtures thereof, orby varying the sizes or shapes of the component particles, or bycombination of the above. Moreover, to achieve desired resistancevalues, two different resistor materials may be blended. Resistors arecreated in through holes by filling the holes with resistor fillcomposition according to the injection method, the sacrificial carriermethod, or conventional methods.

Precision resistors can be achieved using either a laser or abrasivetrimming process after the hole is filled and the fill composition iscured, but prior to copper overplating. In a trimming process, theresistor value is first determined by electrically probing the tworesistor ends, followed by trimming and re-testing. When the hole isfilled using the sacrificial carrier method, the laminated and drilledcopper foil on the top and bottom of the board serves as a mask for thelaser or abrasive trimming, so the excess resistor fill composition isremoved from the hole, but not elsewhere. Such trimming results in areduction in the resistor length, and thus a reduction in resistance.

The resistor-in-hole process can be used to produce solder ballconnections on top or bottom of the plated resistor ends. Fillingapertures with the resistor fill composition is generally done prior tothrough hole plating. Preferably, the resistors in through holes areused for producing large quantities of isolated terminating resistors asare required by emitter coupled logic type applications.

In addition to providing cost reductions, board surface area reductions,reliability enhancements and electrical performance enhancements overconventional discrete resistor assembly technologies, the resistor in athrough hole presents other advantages over conventional planar andburied resistor technologies. These advantages include lower productioncost, and improved resistor tolerance. This resistor design can also beutilized for high reliability applications where it is desirable toperform a leakage test between adjacent electrical nets, by fillingdesired holes with resistor fill composition after leakage testing innewly drilled through holes. When performed as a final process, theresistor ends can be capped by either covering the resistor ends with aconductive, solderable epoxy material or plated to provide a pad atopthe exposed end of the resistor. Such plating may be by conventionalmethods or by the overplating methods disclosed herein.

EXAMPLES OF FILL COMPOSITION Example 1

A cycloaliphatic epoxy fill composition was prepared by combining: about4.25 parts by weight of 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate designated ERL-4221 from Union Carbide; about 4.31 parts byweight of methyl-hexahydrophthalic anhydride; about 1.12 parts by weightof Tone 0231 from Union Carbide; about 0.326 parts by weight of2-ethyl-4-methyl imidazole; about 1.17 parts by weight of Poly Bd-605from Elf Atochem North America Inc., and about 100.86 parts by weight ofcopper powder from Alcan Powder and Pigments having a particle size lessthan 10 microns. Vias in cards were filled with this composition usingthe injection method. The composition was cured at about 140° C. forabout 1.5 hours. The filled vias were then overplated according to thefollowing overplating methods. A portion of the vias were overplated byfirst seeding the surface with Shipley electroless bath followed byconventional acid plating using a Shipley acid copper plating bath.Another portion was overplated by seeding the surface with Pd/Sncolloidal followed by electroless copper plating using shipley C3000.The cards containing the filled vias were evaluated in solder ballconnect technology by being run through 2650 cycles ATC testing from2-80 C.; no failures were noted. In addition three repetitions of soldershock testing revealed no failures. Another portion of the vias wereplated using the copper in the fill composition as the seed layer forelectroless plating; such overplating method adequately plated thefilled vias.

Example 2

A cycloaliphatic epoxy fill composition was prepared by combining: about4.32 parts by weight of ERL-4221, a3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate from UnionCarbide; about 4.16 parts by weight of hexahydrophthalic anhydride;about 1.08 parts by weight of Tone 0231 from Union Carbide; about 0.052parts by weight of benzyl dimethyl amine; about 1.06 parts by weight ofPoly Bd-605, from Elf Atochem North America Inc., and about 42.36 partsby weight of copper powder from Metz Metallurgical Corporation having aparticle size less than 4 microns. Plated through holes were filled withthis composition using the injection method. The composition was curedin an oven at about 140°-150° C. for about 2 hours.

Example 3

A cycloaliphatic epoxy fill composition was prepared by combining: about4.4 parts by weight of ERL-4221, a3,4-3-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate from UnionCarbide, about 4.00 parts by weight of methylhexahydrophthalicanhydride; about 1.15 parts by weight of Tone 0231 from Union Carbide;about 0.072 parts by weight of benzyl dimethyl amine; about 1.20 partsby weight of Poly-Bd 605 from Elf Atochem North America Inc., and about31.77 parts by weight of copper powder from Alcan Powder and Pigmentshaving a particle size less than 10 microns. Plated through holes werefilled with this composition using the injection method, and cured at140°-160° C. for about 1.5 hours.

Example 4

A cycloaliphatic epoxy fill composition was prepared by combining: about4.50 parts by weight of ERL-4221, a3,4-3-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate from UnionCarbide; about 4.34 parts by weight of methylhexahydrophthalicanhydride; about 1.08 parts by weight of Tone 0231 from Union Carbide;about 0.11 parts by weight of benzyl dimethyl amine; and about 45.36parts by weight of Copper powder from Alcan Powder and Pigments having aparticle size less than 10 microns. The composition was used in fillingplated through holes using the injection method. The composition wasthen cured at 140°-160° C. for about 2 hours.

Example 5

A novolac epoxy fill composition was prepared by combining: 20.18 partsby weight of an epoxy novolac designated 8212 from Ciba-Geigy andcontaining about 30% methyl ethyl ketone; about 55.4 parts by weight ofcopper powder from Alcan Powders and Pigments; 0.18 parts by weight of asurface treating agent, specifically, a silane coupling agent Z-6040from Dow-Corning and about 0.045 parts by weight 2-ethyl-4-methylimidazole. About 10 parts by weight of methyl ethyl ketone was added toprovide the proper viscosity to coat 1 oz. copper foil for filling thevias according to the sacrificial carrier method. Foils having differentcoating thickness from 0.002, 0.004, 0.0065 inches were used. Varioussubstrates, such as an FR-4 circuit board with thickness, 0.040, 0.060,0.100 inches, and various via diameter: 0.004-0.012 (0.002 increments)inches in pattern: 8×1.5 inch (1000 vias) per via size were placed inthe lamination press with the mask aligned to the hole pattern in thesubstrate. The sacrificial carrier was placed with the coated sideagainst the polyamide mask. The entire package was then placed undervacuum for 7 minutes prior to heating. The lamination pressure wasmaintained at 150 psi with a peak temperature of 185° C. for 2 hours.

All combinations of substrate, via diameter and coating thicknesscompletely filled the vias. Panels having filled vias were overplated byfirst seeding the surface followed by electroless copper plating usingShipley C3000.

Example 6

A cyanate ester fill composition was prepared by combining: about 7.6parts by weight of Bisphenol AD dicyanate from Ciba-Geigy Corporationunder the designation Arocy L10; about 43.5 parts by weight of copperpowder from Alcan Powders and Pigments; and about 0.25 parts by weightof zinc octanoate. Vias were filled using this composition employing theinjection method and cured at temperatures of about 200°-220° C. forabout 3 hours under nitrogen.

Example 7

A cyanate fill composition was prepared by combining: about 7.6 parts byweight of Arocy L10, a Bisphenol AD dicyanate from Ciba-GeigyCorporation; about 2.5 parts by weight of EPON 828 from Shell Chemical;about 43.5 parts by weight of Copper powder from Alcan Powders andPigments; and about 0.25 parts by weight of zinc octanoate. Vias werefilled with this composition employing the injection method and thecomposition was then cured at about 180°-190° C. for about 2 hours.

Example 8

A cyanate fill composition was prepared by combining: about 7.6 parts byweight of Arocy L10, a Bisphenol AD dicyanate from Ciba-GeigyCorporation; about 3.5 parts by weight of ECN-1280 a cresol novolakepoxy resin from Ciba-Geigy; about 44.5 parts by weight of copper powderfrom Alcan Powders and Pigments; and about 0.25 parts by weight of zincoctanoate. Vias were filled with this composition employing theinjection method and the composition was cured at about 175°-195° C. forabout 2 hours.

Example 9

A cyanate fill composition was prepared by combining: about 7.6 parts byweight of Arocy L10, a Bisphenol AD dicyanate from Ciba-GeigyCorporation, about 2.5 parts of dinonyl phenyl cyanate; about 43.5 partsby weight of copper powder from Alcan Powders and Pigments; and about0.25 parts by weight of zinc octanoate. Vias were filled with thiscomposition employing the injection method and the composition was curedat about 160°-190° C. for about 2 hours.

Example 10

A cyanate fill composition was prepared by combining: about 8.5 parts byweight of RTX-366, a Bisphenol M dicyanate from Ciba-Geigy, about 1.5parts by weight of Bisphenol AD dicyanate; about 45.3 parts by weight ofcopper powder from Alcan Powders and Pigments; about 0.2 parts by weightof zinc octanoate and about 20 parts by weight of methyl ethyl ketone.The composition was coated onto a sacrificial 1 oz copper foil, airdried and partially cross-linked in an oven at 140° C. for 3-4 minutesand evaluated as in Example 5.

Example 11

A cyanate fill composition was prepared by combining: about 8.2 parts byweight of Arocy L10 as Bisphenol AD dicyanate from Ciba-GeigyCorporation; about 2.5 parts by weight of EPON 828 from Shell Chemical;about 45.5 parts by weight of copper powder from Alcan Powders andPigments; about 0.25 parts by weight of zinc octanoate; and about 30parts by weight of methyl ethyl ketone. The composition was coated ontoa sacrificial 1 oz copper foil, air dried and b-staged at 140° C. for3-4 minutes and evaluated as in Example 5.

All combinations of substrate, via diameter and coating thicknessexhibited complete filling of the vias.

Example 12

An epoxy novolac fill composition was prepared by combining about 30.6parts by weight of 8212 an epoxy cresol novolac epoxy resin fromCiba-Geigy (in about 30% methyl ethyl ketone); about 63.6 parts byweight of copper powder from Alcan Powders and Pigments, about 0.22parts by weight of the silane coupling agent Z-6040 from Dow-Corning;about 0.03 parts by weight 2-ethyl-4-methyl imidazole and about 20.5parts by weight of Vulcan P, a carbon black from Cabot Corporation.About 10 parts by weight of methyl ethyl ketone was added to provide theproper viscosity to coat the 1 oz copper foil for filling the viasaccording to the sacrificial carrier method. The electrical resistivityof the epoxy composition was 0.128 ohm-inches. Foils having differentcoating thickness from 2-3 mils were made.

The substrates, such as an FR4 circuit board with thickness, 60 mils,and nonplated vias of diameter: 0.014 mils in pattern: 8×1.5 inch (1000vias) were placed in the lamination press with the mask aligned to thehole pattern in the substrate. The sacrificial carrier was placed withthe coated side against the polyamide mask. The entire package was thenplaced under vacuum for 7 minutes prior to heating. The laminationpressure was maintained at 150 psi with a peak temperature of 185° C.for 2 hours. All vias were completely filled. Next the board wasdrilled, seeded with palladium tin colloid, conventionally acid copperplated and circuitized thus leaving each end of the resistor capped witha plated copper. Resistors in holes had an average resistance of 50ohms.

Example 13

An epoxy novolac fill composition was prepared by combining 20.6 partsby weight of 8212 from Ciba-Geigy in about 30% methyl ethyl ketone;about 37.5 parts by weight of Black Pearls 2000, a carbon powder fromCabot Corporation; about 0.2 parts by weight of silane coupling agentZ-6040 from Dow-Corning; and about 0.045 parts by weight2-ethyl-4-methyl imidazole. About 10 parts by weight of methyl ethylketone was added to provide the proper viscosity to coat the 1 oz copperfoil for filling the vias according to the sacrificial carrier method.Foils having different coating thickness from 2-3 mils were made. Thefoils were laminated with an FR4 circuit board as described in Example12.

Example 14

A cycloaliphatic epoxy fill composition was prepared by combining: about4.4 parts by weight of ERL-4221, a3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate from UnionCarbide; about 4.0 parts by weight of methylhexahydrophthalic anhydride;about 1.11 parts by weight of Tone 0231 from Union Carbide; about 0.296parts by weight of 2-ethyl-4-methyl imidazole; about 0.9 parts by weightof Poly Bd-605, a flexiblizer, from Elf Atochem North America, Inc.;about 43.86 parts by weight of copper powder from Alcan Powder andPigments having a particle size less than 10 microns; and about 11 partsby weight of Vulcan XC72, a carbon black from Cabot Corporation. Thepreceding materials were combined using a low shear mixer, degassed in avacuum desiccator and placed in a freezer for testing. Subsequently,this composition was used in filling the vias using the injection methodand cured at about 140° C. for about 2 hours.

Example 15

A cyanate ester fill composition was prepared by combining: about 6parts by weight of Arocy L10, a Bisphenol AD dicyanate from Ciba-GeigyCorporation; about 4.5 parts by weight of EPON 828 from Shell Chemical;about 30.5 parts by weight of copper powder from Alcan Powders andPigments; about 6 parts by weight of Vulcan P, a carbon black from CabotCorporation; and about 0.10 parts by weight of zinc octanoate. Vias weresubsequently filled using this composition employing the injectionmethod and cured at about 180° C. for about 1.5 hours.

Example 16

A cyanate fill composition was prepared by combining about 6 parts byweight of RTX-366, a Bisphenol M dicyanate from Ciba-Geigy Corporation;about 6 parts by weight of Arocy L10, a Bisphenol AD dicyanate fromCiba-Geigy Corporation; about 4.3 parts by weight of copper powder fromAlcan Powders and Pigments; about 9 parts by weight of Vulcan XC72, acarbon black from Cabot Corporation; and about 0.15 parts by weight ofzinc octanoate. Vias were subsequently filled using this compositionemploying the injection method and cured at about 185° C. for about 2hours.

The above examples 2-16 all filled the vias completely.

While the invention herein has often been described as relating to theattachment of solder ball connect modules, it is also applicable forattachment of other surface devices such as conventional surface mountcomponent leads or direct chip attach C-4 solder joints.

What we claim is:
 1. A method of forming a resistor in a circuit carriercomprising the steps of:a. providing a circuit carrier having at leastone aperture; b. filling the aperture with a resistor fill compositionto provide a resistor with exposed ends; c. measuring the resistance ofthe resistor; and d. trimming the resistor to provide a desiredresistance values; e. selective overplating the exposed ends of theresistor to provide a pad over the aperture.
 2. The method of claim 1,wherein the fill composition comprises metal and in step e, the metal isused as a seed layer to overplate the filled aperture.
 3. A method offorming a resistor having a resistance value, in a circuit carrier,comprising the steps of:a. providing a circuit carrier having at leastone aperture of known dimensions or volume; b. calculating a materialresistivity value required to produce the resistance value according tothe formula:

    Rho=R<L/A

Where:R=Resistance Value in ohms Rho=Material Resistivity in ohm-inchesL=Resistor Length=Board Thickness A=Cross-sectional Area c. providing afill composition of the material resistivity value calculated in step b;and d. filling the aperture with the resistor fill composition; e.selectively overplating the exposed ends of the resistor to provide apad over the aperture.